Installations for pre-heating air in marine and industrial boiler plants, dust-removing apparatus included in Class 11, apparatus for washing gas, steam cooling palnt, drum-type heating apparatus included in Class 11 for asphalt mixing plant, silos incorporating heating apparatus, for use in bituminous road marking; cetrifugal and axial flow fans, electrofilters, smoke gas pipings, air pipes, tin flues, all being parts of installations included in Class 11